Low‐volume spraying to control coffee leaf rust in Kenya

SUMMARY In a 2‐year trial on arabica coffee in Kenya, a cuprous oxide fungicide (50% Cu) at a range of 0–5% (w/w) was applied by mist‐blower five times a year at approximately 10 gal./acre. The results demonstrated: (i) a positive linear relationship between log. spray concentration and the amount of copper (expressed as log 10 mg. Cu/m. 2 +1) retained by the foliage; (ii) a significant negative linear relationship between spray concentration and the incidence of leaf rust (caused by Hemileia vastatrix Berk. & Br.); (iii) a positive linear relationship between concentration of fungicide applied and yield of coffee. An additional spray in May increased the mean annual yield by 2 cwt. coffee per acre and reduced a heavy rust attack. Trees receiving the highest spray concentration retained the most leaves; at lower concentrations there was considerable leaf fall but this was offset by new leaf production; unsprayed trees suffered severe leaf loss and were unable to produce as much new foliage.